In a passive optical network (Passive Optical Network, PON for short) system, one optical line terminal (optical line terminal, OLT for short) is connected to a plurality of optical network units (optical network unit, ONU for short).
In an actual environment, a distance between each ONU and the OLT differs greatly, and light attenuation of each ONU varies. Therefore, there is a large difference between optical power of ONUs received by a same OLT port, and there is also a large difference between optical power that is of the OLT and that is received by ONUs of a same OLT port. As a result, a receiving part of an optical module in the OLT or the ONU needs to support a relatively large optical power receiving range to adapt to application in the actual environment.
Currently, in the PON system, an optical power receiving range of the OLT is from −8 dBm to −28 dBm, and an optical power receiving range of the ONU is from −8 dBm to −27 dBm. However, in actual application, optical power receiving ranges of most OLTs or ONUs reach a threshold of the foregoing range or exceed the foregoing range due to an actual environment, a component arrangement, and the like, resulting in service interruption.
Currently, FIG. 1 shows an optical module in an OLT or an ONU (only a receiving part is shown). The optical module includes an optical signal receive end, an avalanche photodiode, a transconductance amplifier, and a feedback resistor R1. The optical signal receive end is connected to a negative electrode of the avalanche photodiode, a positive electrode of the avalanche photodiode is connected to a negative input end of the transconductance amplifier, a first end of the feedback resistor R1 is connected to the negative input end of the transconductance amplifier, a second end of the feedback resistor R1 is connected to an output end of the transconductance amplifier, and a positive input end of the transconductance amplifier is grounded.
After receiving an optical signal, the optical signal receive end transmits the optical signal to the avalanche photodiode. The avalanche photodiode generates an optical current I after receiving the optical signal. A value of the optical current is in direct proportion to an optical intensity value of the received optical signal. The avalanche photodiode transmits the optical current I to the negative input end of the transconductance amplifier. The transconductance amplifier generates an output voltage Uout=I*R1 after the optical current I passes through the transconductance amplifier and the feedback resistor R1. The output voltage is provided for a subsequent limiting amplifier to perform voltage amplitude processing.
However, the receiving part of the optical module has the following disadvantage: Because configuration of the feedback resistor R1 is fixed in a product, an optical power receiving range of the receiving part of the optical module is also fixed. However, in actual application, optical power received by the OLT or the ONU may exceed the fixed optical power range, resulting in a bit error in actual application.